An image quality of X-ray images generally may be limited in X-ray detectors and/or in X-ray imaging systems with a variable source-image-distance. In order to improve the image quality, usually an anti-scatter device comprising an anti-scatter grid is utilized, which allows to increase a contrast in the X-ray image by reducing an incidence of scattered radiation upon a reception area of the X-ray detector.
Examples of such X-ray system is for instance a C-arm system, in which an assembly comprising an X-ray detector and an anti-scatter device and/or an anti-scatter grid may be moved closer to and/or further away from an X-ray source. In other X-ray imaging systems with variable source-image-distance the X-ray source may be moved closer to and/or further away from an assembly comprising a table and an X-ray detector with anti-scatter device depending on application demands and/or requirements. In all these systems, usually a less than optimal anti-scatter grid ratio needs to be chosen to reduce the detrimental effects of shading artifacts caused by the grid when operated with a source-image-distance differing from its nominal focal distance. In the international norm IEC60627 the application limits for given grid parameters are provided and these limits should be matched with customer wishes for the range of allowed source-image-distances.
A potential solution to this issue may be to have a variable focused anti-scatter grid in which a focal distance and/or a focusing distance may be matched to the actual source-image-distance for a certain range of source-image-distances. For such grids a higher aspect ratio, as defined in IEC60627, may be chosen which may reduce the amount of scattered radiation in the X-ray image and thus may improve the image quality.
Normally, an anti-scatter device and/or an anti-scatter grid comprises a stack of lead lamellae interspaced with an X-ray transparent interspacer material, such as air, an organic material and/or Aluminum, which positions each lead lamella in an orientation directed towards a focal spot of the anti-scatter device and/or the anti-scatter grid at a distance equal to the focal distance and/or the focusing distance. Further, the anti-scatter device and/or the anti-scatter grid may be covered with a carbon fiber or an aluminum cover element to give the grid sufficient stiffness and to protect the interior against moisture and harm.
In document U.S. Pat. No. 5,291,539 A a variable focused anti-scatter grid is disclosed having a flexible elongated slatted grid structure, which is suspended between a pair of spaced apart grid support frames each of which is adapted for rotation about a transverse axis intermediate the suspended ends of the grid. A mechanical adjustment means provides equal but opposite angular motion of the frames to curve the grid along a circular path.